Non‐thermal DNA damage of cancer cells using near‐infrared irradiation

Previously, we reported that near‐infrared irradiation that simulates solar near‐infrared irradiation with pre‐ and parallel‐irradiational cooling can non‐thermally induce cytocidal effects in cancer cells. To explore these effects, we assessed cell viability, DNA damage response pathways, and the percentage of mitotic cancer cells after near‐infrared treatment. Further, we evaluated the anti‐cancer effects of near‐infrared irradiation compared with doxorubicin in xenografts in nude mice by measuring tumor volume and assessing protein phosphorylation by immunoblot analysis. The cell viability of A549 lung adenocarcinoma cells was significantly decreased after three rounds of near‐infrared irradiation at 20 J ⁄ cm2. Apoptotic cells were observed in near‐infrared treated cells. Moreover, near‐infrared treatment increased the phosphorylation of ataxia‐telangiectasia mutated (ATM) at Ser1981, H2AX at Ser139, Chk1 at Ser317, structural maintenance of chromosome (SMC) 1 at Ser966, and p53 at Ser15 in A549 cells compared with control. Notably, near‐infrared treatment induced the formation of nucleic foci of γH2AX. The percentage of mitotic A549 cells, as measured by histone H3 phosphorylation, decreased significantly after three rounds of near‐infrared irradiation at 20 J ⁄cm2. Both near‐infrared and doxorubicin inhibited the tumor growth of MDA‐MB435 melanoma cell xenografts in nude mice and increased the phosphorylation of p53 at Ser15, Chk1 at Ser317, SMC1 at Ser966, and H2AX at Ser139 compared with control mice. These results indicate that near‐infrared irradiation can non‐thermally induce cytocidal effects in cancer cells as a result of activation of the DNA damage response pathway. The near‐infrared irradiation schedule used here reduces discomfort and side effects. Therefore, this strategy may have potential application in the treatment of cancer. (Cancer Sci, doi: 10.1111/j.1349‐7006.2012.02310.x, 2012)